Neutrophils migrate from the blood to the site of inflammation in response to agents liberated at the site, termed chemotactic factors, such as FMLP and C5a. These factors form a complex with specific receptors of neutrophils that initiate a series of biochemical and morphological events. These processes are dependent on the integrity of cellular plasma membranes, the submembrane microfilaments, and cytoplasmic microtubules. Cytoskeletal rearrangement accompanied by phosphorylation of cytoskeletal 2 protein plays a major role in the cell activation process in neutrophils. Cells were labeled with p, the phosphoprotein were isolated and separated by electrophoresis, followed by autoradiography, the results were then quantitated using a densitometer. The results show a minimum of 12-15 phosphorylated cytoskeletal proteins with the MW ranging from approximately 20 to 180 Kd. Addition of FMLP and PMA results in the formation of phosphoprotein patterns different from those formed in the presence of cAMP-mediated agonists such as isoproterenol, indicating separate phosphorylation pathways for chemotactic factors. One particular phosphoprotein with a MW of approximately 55kd is phosphorylated by FMLP and PMA only, and is distributed in triton X-100 soluble and insoluble extract. The identification of this phosphoprotein Is under investigation . It would be intriguing to know its relationship with tubuline protein and whether FMLP mediates translocation of this protein during cell activation. Results from the studies of mechanism of cAMP formation in leukocytes would complement and would be helpful in further identification of particular cytoskeletal protein being phosphorylated during the chemotaxis.